Heretofore, as a reinforcing material for GRC, an SiO2—ZrO2—R2O (R is Li, Na, K)-based ZrO2-containing alkali-resistant glass fiber as described in Patent Document 1 has been used.
Moreover, the glass fiber has been also used as a reinforcing material for calcium silicate board and as a corrosion-resistant material for battery separators or the like.
The glass fiber as mentioned above is, for example, used in a fiber form, which is obtained by continuously forming and drawing a molten glass into a fiber using a noble metal-made bushing apparatus. Incidentally, the structure of the bushing has a container shape for the purpose of retaining the molten glass and a large number of nozzles are disposed on the bottom in the vertical direction. The glass fiber is formed by drawing the molten glass adjusted to a temperature around a forming temperature (a temperature that is also called a drawing temperature and at which the viscosity of the glass becomes about 103 dPa·s) from the nozzle on the bushing bottom in a fiber form.